Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$40.57	3.550%	$42.0102	$42.01	$42.00	$42.00
Purchase #2	$214.26	9.150%	$233.8648	$233.86	$233.85	$233.90
Purchase #3	$228.35	3.535%	$236.4222	$236.42	$236.40	$236.40
Purchase #4	$213.83	9.792%	$234.7682	$234.77	$234.75	$234.80
Purchase #5	$141.44	7.804%	$152.478	$152.48	$152.50	$152.50
Purchase #6	$154.72	10.282%	$170.6283	$170.63	$170.65	$170.60
Purchase #7	$35.64	6.467%	$37.9448	$37.94	$37.95	$37.90
7 purchase totals =	$1,028.81		$1,108.1165	$1,108.11	$1,108.10	$1,108.10